Probabilistic Analysis of the Tsunami Disaster on the Vulnerability Level of Buildings in Painan City, West Sumatra based on the Earthquake Ratio with the Logic Tree Method

Abstract

Indonesia is an archipelagic country stretching from Sabang to Merauke and is located at the convergence of the most complex and active tectonic plates in the world, namely Eurasia, Indo-Australia, and the Pacific. One of the regions with a high probability of earthquakes and high tsunamis is the island of Sumatra, which lies between the Eurasian and Indo-Australian plates. Painan city is located in West Sumatra Province, where it is surrounded by three megathrust zones: the Nias-Simeulue segment, Mentawai-Siberut segment, and Mentawai-Pagai segment. These three megathrust zones, namely Nias-Simeulue with an estimated earthquake magnitude of 8.7 Mw, Mentawai-Siberut with an earthquake magnitude of 8.9 Mw, and Mentawai-Pagai with an earthquake magnitude of 8.9 Mw, can potentially cause tsunamis that may reach Painan city. The aim of this study is to investigate the influence of seismic activity level variables and the ratio between large and small earthquakes on tsunami wave height using the logic tree method, assess the tsunami hazard potential using Probabilistic Tsunami Hazard Assessment (PTHA), and evaluate the vulnerability of existing buildings in Painan city. Tsunami simulations in this study were conducted using the Cornell Multigrid Coupled Tsunami (COMCOT) program, which applies the Shallow Water Equation (SWE). Additionally, the Building Tsunami Vulnerability (BTV) equation was used to calculate the vulnerability index of buildings based on their conditions and tsunami wave heights. The calculation of the BTV value for the tsunami height parameter was modified using fragility curves that depict the relationship between force and the probability of tsunami wave damage. From the simulation results, the tsunami height was obtained, which in turn determines the probability of tsunami hazard on buildings with return periods of 1000 and 4000 years. After the simulations, the Building Tsunami Vulnerability (BTV) calculation was performed to determine the vulnerability level of buildings to tsunamis.